But critics are skeptical. A New York Times editorial notes that the clause will "create confusion and wreak havoc in classrooms" by giving students the power to refuse completing or participating in any assignments that they claim violates their religious beliefs. It permits students who believe in creationism, for instance, to decline any assignments on evolution.

McGhee, however, says doesn't anticipate any instances where a student might claim "it's against my religion to do algebra."

The move in Missouri is in part seen as one of several pieces of state legislation nationwide that allows for more room for religion and intelligent design in public schools. The Tennessee state Senate passed a bill in March that protects teachers who allow student to question and criticize "controversial" scientific theories like evolution. Indiana legislators in January moved forward on a bill that would allow school districts to decide whether to include creationism alongside teachings of evolution in science curriculum.

Research from two Pennsylvania State University professors revealed last year that the majority of public school biology teachers in the U.S. shy away from teaching evolution because they're either unwilling or unprepared to teach it: some advocate creationism while others are afraid to address the topic for fear of controversy.

According to results of the 2009 National Assessment of Educational Progress, a federal test known as the Nation's Report Card, less than half of U.S. fourth-, eighth- and 12-th grade students were considered proficient in science.